The present invention relates to electrical circuits, and more particularly, to a integrated electrical circuits.
In some integrated circuits (ICs), complicated circuit components operating with various signals and information may be integrated. An IC may use one or more clock signals to control complicated operations of the circuit components and adjust operating timings thereof. In applications of communication, signal processing, and the like, the IC may use signal sources and signal source generators as well as the clock signals. Circuit designers may benefit from a clock generation circuit and a signal source circuit that can be adapted to various circuits, processes, user applications, and/or variables such voltage and temperature, among others. A clock signal or reference signal can be generated by using various circuits including inverters and ring oscillators.
Reference is now made to FIG. 1, which is a graph illustrating an inversely-proportional-to-absolute-temperature (IPTAT) characteristic. As illustrated, the IPTAT characteristic may denote that a value is changed inversely proportional to a temperature. Referring to graph 101, a frequency may change inversely proportional to a change in temperature.
Reference is now made to FIG. 2, which is a graph illustrating a proportional-to-absolute-temperature (PTAT) characteristic. The PTAT characteristic may denote that a value is changed proportional to a temperature. Referring to graph 105, a frequency may change proportional to a temperature.
Reference is now made to FIG. 3, which is a circuit diagram illustrating a general ring oscillator 200. The ring oscillator 200 may include an odd number of inverters 221, 222, and 225. A general ring oscillator 200 may have a disadvantage in terms of generating a clock signal. For example, a delay time of each inverter may be increased according to an increase in temperature. The increase in delay time may lead to an increase in clock signal generating period T. Therefore, as the delay time is increased, the operating frequency of the ring oscillator may be disadvantageously lowered. Accordingly, the operating frequency characteristic of the ring oscillator 200 may be expressed by the aforementioned IPTAT characteristic shown in FIG. 1.
Inverters and/or a ring oscillator may have a large dependency on a temperature. Therefore, if the increase in delayed amount is not compensated according to an increase in temperature, the ring oscillator may not be normally operated.
In order to compensate for a change in characteristics of the ling oscillator according to a temperature, a method of increasing bias voltages of MOS transistors of the inverters has been proposed. More specifically, the increase in delayed amount according to a temperature may be prevented by applying increased bias voltages to the MOS transistors of the inverters. However, the method of increasing bias voltages may include limitations corresponding to low voltage operation and/or a high-speed operation.
A biased ring oscillator may allow only low voltage input and output. That is, high voltage signals may not be input to or output from the biased ring oscillator. In addition, since the biased ring oscillator may not be operated in a high frequency band, an operating period thereof may be increased. In this regard, a high speed operation may not be obtained. As an example, in a 70 nm DRAM, if a bias voltage of 1.35V is applied, a maximum operating frequency may be 1 MHz. That is, the DRAM may be inoperable at a frequency higher than 1 MHz.